經(jīng)皮電刺激神經(jīng)療法(TENS)原理

經(jīng)皮電刺激神經(jīng)療法（TENS）原理TENS 經(jīng)皮電刺激神經(jīng)療法 經(jīng)皮電刺激神經(jīng)療法是用電來刺激有疼痛癥狀的特定的興奮感覺神經(jīng)和刺激閘門機(jī)制和（或）內(nèi)源性的阿片肽（如腦啡肽）系統(tǒng)。TENS的應(yīng)用方法因這些生理作用機(jī)制的不同而不同。TENS不能保證完全達(dá)到止痛的目的，并且疼痛得到緩解的病人百分率也是會(huì)改變的，但一般情況下，急性疼痛的緩解率在65左右，慢性疼痛則在50左右。但這些方法都要強(qiáng)于醫(yī)用的安慰劑。這種方法是非侵入性的，并且相比較藥物治療，他幾乎沒有副作用。最常見的問題就是皮膚的過敏性反應(yīng)（大約有23的病人），這些幾乎經(jīng)常是由于電極的材料，傳導(dǎo)膠體或者是固定電極的綁帶引起的。目前大部分TENS的電極是采用自粘性，預(yù)涂膠體的電極做成。這種自粘性電極有以下幾個(gè)優(yōu)點(diǎn)，減少交叉感染的風(fēng)險(xiǎn)，易于使用，更低的過敏發(fā)生率和更低的成本。機(jī)械參數(shù)在描述TENS是如何用于完成鎮(zhèn)痛作用之前，先對(duì)現(xiàn)代機(jī)器的可獲得的主要的治療變量做一個(gè)概述。下圖是一臺(tái)典型TENS的控制器。 電流強(qiáng)度（A）（強(qiáng)度）一般在080mA的范圍內(nèi)，可是有些機(jī)器或許可以輸出100mA的電流。雖然這個(gè)機(jī)器輸出的是小電流，但已經(jīng)足夠了，因?yàn)樗闹饕饔脤?duì)象是感覺神經(jīng)，只要有足夠的電流通過組織，使感覺神經(jīng)去極化，這種治療方式就是有效的。 這臺(tái)機(jī)器可以傳送脈沖電流，傳送這些脈沖的頻率（脈沖頻率B）通常在12個(gè)脈沖每秒到200或者250個(gè)脈沖每秒間變化。要產(chǎn)生臨床有效的治療效應(yīng)，建議TENS應(yīng)該涵蓋2150HZ的頻率。 除刺激頻率以外，每個(gè)脈沖的持續(xù)時(shí)間（或?qū)挾龋┰?0250s間變化，最近的證據(jù)表面，相比強(qiáng)度和頻率，脈沖寬度重要性要小。 另外，現(xiàn)代的機(jī)器提供了一個(gè)burst模式（D），使得脈沖可以以爆破或者長隊(duì)的形式輸出，通常在23個(gè)burst每秒的速率。最后，調(diào)制模式（E）可提供所采用的方法，使輸出的脈沖不規(guī)則，因此盡量減少了因規(guī)則刺激造成的機(jī)體適應(yīng)效應(yīng)。之所以用如此短的脈沖來實(shí)現(xiàn)這些效果，是因?yàn)樽饔脤?duì)象是感覺神經(jīng)，而且往往是有較低的閾值（即他們是很容易興奮的），并認(rèn)為他們會(huì)回應(yīng)快速變化的電狀態(tài)。一般不需要用較長的脈沖去使神經(jīng)去極化，因此，小于一毫秒的刺激是足夠的。大部分機(jī)器提供兩通道，兩副電極可以同時(shí)刺激。在某些情況下，這是一個(gè)明顯的優(yōu)勢，盡管有意思的是大部分的病人和治療師趨向于應(yīng)用單通道。不同的廠家生死的TENS產(chǎn)生的脈沖波會(huì)不同，但往往是不對(duì)稱的改良的雙相方波脈沖。雙相性脈沖意味著通常沒有凈直流電成分，從而避免了由于電極下的點(diǎn)解產(chǎn)物的堆積所造成的皮膚反應(yīng)。作用機(jī)理這種類型的刺激旨在刺激感覺神經(jīng)，這樣一來，啟動(dòng)特異的自然鎮(zhèn)痛機(jī)制。為了方便起見，如果認(rèn)為有兩個(gè)主要的鎮(zhèn)痛機(jī)制，可以激活閘門控制機(jī)制和內(nèi)源性的阿片系統(tǒng)，要考慮到刺激這兩個(gè)不同的系統(tǒng)所需的參數(shù)是有差異的。用閘門控制機(jī)制來鎮(zhèn)痛的方法涉及激活感覺纖維，這樣做，減少了從“C”纖維從脊髓向高級(jí)中樞傳輸?shù)挠泻Υ碳?。A纖維似乎正在增加至一個(gè)比較高頻率的刺激（以90130HZ or pps）。很難對(duì)每一個(gè)病人找到一個(gè)產(chǎn)生最好鎮(zhèn)痛效果的單一頻率，但90130HZ這樣的頻率對(duì)于大部分的個(gè)體都適用。另一種方法是刺激纖維，一種以較低頻率（25HZ）刺激會(huì)優(yōu)先作出反應(yīng)的纖維，將啟動(dòng)阿片機(jī)制，并通過脊髓釋放一種內(nèi)源性的阿片（腦磷脂）來鎮(zhèn)痛，從而減輕有害感覺通路的激化作用。第三種可能性是，由雇用burst模式在同一時(shí)間刺激兩種神經(jīng)類型。在這種情況下，較高頻率的刺激輸出（通常在100HZ左右）會(huì)中斷（或爆破）的頻率約為23個(gè)burst每秒。當(dāng)機(jī)器開著，他會(huì)提供100HZ的脈沖，因此激活了纖維和閘門控制機(jī)制，但由于burst的發(fā)生頻率23HZ，會(huì)興奮纖維，從而刺激了阿片系統(tǒng)。對(duì)于某些病人來說，這是到目前為止最有效的鎮(zhèn)痛方法，盡管這有些不可思議，眾多的病人發(fā)現(xiàn)這比其他形式的TENS不容易接受。TENS模式傳統(tǒng)TENS通常使用的刺激相對(duì)較高的頻率（90130HZ），并使用相對(duì)窄的脈沖寬度（開始約100ms），但如上所述，在目前正在進(jìn)行的研究項(xiàng)目文獻(xiàn)中很少由支持脈沖時(shí)間操縱的。刺激以正常的強(qiáng)度傳遞，絕對(duì)有但不會(huì)不舒服。30分鐘或許是最小限度的有效時(shí)間，根據(jù)需要可以盡可能長時(shí)間的延長治療時(shí)間。鎮(zhèn)痛最重要的是在刺激的過程中，并且有一個(gè)有限的延續(xù)效應(yīng)即機(jī)器關(guān)掉后，疼痛仍然可以得到緩解。電針型TENS使用頻率較低的刺激（25HZ）和較寬的脈沖（200250ms）。這種使用強(qiáng)度通常比傳統(tǒng)的TENS強(qiáng)度大，但仍然不是病人的極限，但是相當(dāng)明確的，強(qiáng)有力的感覺。如前所述，30分鐘是有治療效果的最少治療時(shí)間。需要有一段時(shí)間來刺激阿片的分泌達(dá)到足夠的量，因此鎮(zhèn)痛效果的起效可能會(huì)比傳統(tǒng)模式慢。一旦有足夠的阿片釋放，他將在刺激停止后依然持續(xù)發(fā)揮作用。許多病人覺得以低頻率在一天中不時(shí)的刺激是一個(gè)有效的策略。他的延續(xù)作用可能會(huì)持續(xù)好幾個(gè)小時(shí)。短暫強(qiáng)刺激型TENS這是一個(gè)TENS模式，可以用來實(shí)現(xiàn)快速鎮(zhèn)痛，但有些病人可能會(huì)覺得刺激的強(qiáng)度太劇烈，無法堅(jiān)持忍受到出現(xiàn)治療效果的那段時(shí)間。脈沖頻率應(yīng)用高（90130HZ）和脈沖持續(xù)時(shí)間也高（200ms以上）。電流接近于病人容忍的水平，這樣他們就不會(huì)再想把機(jī)器調(diào)的更高。這樣，能量傳遞給病人相對(duì)其他模式時(shí)高。建議在這樣的刺激強(qiáng)度下的治療，1530分鐘是最普遍使用的治療時(shí)間。觸發(fā)模式TENS如上所述，機(jī)器發(fā)送傳統(tǒng)的TENS，但burst模式打開，因此以23burst每秒的頻率發(fā)放來中斷電刺激。刺激強(qiáng)度必須在相對(duì)高的情況下，雖然不如短暫強(qiáng)烈型TENS那樣高，更像電針型lo TENS的強(qiáng)度。頻率的選擇以上各種模式指南，它可能不適合去確定特定的頻率用來達(dá)到某一特定效果。如果用一個(gè)單一的頻率作用于每一個(gè)人，將容易很多，但研究并不支持這個(gè)觀點(diǎn)。病人（或者治療師）需要去發(fā)現(xiàn)最有效的鎮(zhèn)痛頻率，操作頻率盤或按鈕是最好的發(fā)現(xiàn)最佳頻率的方法，如果不進(jìn)行調(diào)節(jié)把盤和按鈕放置一邊，這樣的話很難達(dá)到最佳效果。刺激強(qiáng)度如上面發(fā)現(xiàn)的，不可能用多少微安來描述治療電流強(qiáng)度。最有效的強(qiáng)度指標(biāo)是參照病人在治療時(shí)的感覺。通常來說，Hi TENS的治療強(qiáng)度是讓患者有明確的但無痛的刺激感，Lo TENS的治療強(qiáng)度則是強(qiáng)烈的但無痛的刺激感。電極放置：對(duì)于這種治療方法，為了獲得最大的治療效益，把刺激電極放置在疼痛的相應(yīng)脊髓水平。把電極放置在損傷的任何一側(cè)或疼痛區(qū)域，以獲得最好的鎮(zhèn)痛效果，是最常見的做法。研究還報(bào)道了其他一些有效的放置方法，大多數(shù)是放置在相當(dāng)?shù)纳窠?jīng)根水平：刺激適當(dāng)神經(jīng)根刺激外周神經(jīng)刺激運(yùn)動(dòng)點(diǎn)刺激觸發(fā)點(diǎn)或針刺點(diǎn)刺激適當(dāng)?shù)模ㄍ患股窠?jīng)支配的）皮區(qū)，肌肉區(qū)，骨區(qū)如果疼痛的來源是模糊的，散在的或者是特別廣泛的，可以同時(shí)使用兩個(gè)通道，2通道應(yīng)用也可以有效的處理局部牽涉痛的聯(lián)合疼痛，每一個(gè)通道用于一個(gè)部位。禁忌癥不理解物理治療師的指導(dǎo)的病人或者不協(xié)作的病人孕婦的軀干，腹部或骨盆。TENS用于產(chǎn)痛例外。帶起搏器的病人對(duì)電極，凝膠體或綁帶有過敏反應(yīng)的病人皮膚條件：比如皮炎，濕疹病人目前或者最近出血或有循環(huán)障礙，比如組織局部出血，血栓及相關(guān)條件電極放在頸部或頸動(dòng)脈竇注意事項(xiàng)如果有反常的皮膚反應(yīng)，電極要放在更適宜的位置確保有效的刺激電極不能放在眼部患有癲癇癥的病人需咨詢相關(guān)醫(yī)生，并由治療師做出判斷避免兒童的骨骺活躍區(qū)在分娩時(shí)使用腹部電極會(huì)干擾胎兒的監(jiān)測設(shè)備Transcutaneous Electrical Nerve Stimulation (TENS) TENS is a method of electrical stimulation which primarily aims to provide a degree of pain relief (symptomatic) by specifically exciting sensory nerves and thereby stimulating either the pain gate mechanism and/or the opioid system. The different methods of applying TENS relate to these different physiological mechanisms. Success is not guaranteed with TENS, and the percentage of patients who obtain pain relief will vary, but would typically be in the region of 65%+ for acute pains and 50%+ for more chronic pains. Both of these are better than the placebo effect.The technique is non invasive and has few side effects when compared with drug therapy. The most common complaint is an allergic type skin reaction (about 2-3% of patients) and this is almost always due to the material of the electrodes, the conductive gel or the tape employed to hold the electrodes in place. Most TENS applications are now made using self adhesive, pre gelled electrodes which have several advantages including reduced cross infection risk, ease of application, lower allergy incidence rates and lower overall cost.Machine parameters:Before attempting to describe how TENS can be employed to achieve pain relief, the main treatment variables which are available on modern machines will be outlined. The location of these controls on a typical TENS machine is illustrated in the diagram.The current intensity (A) (strength) will typically be in the range of 0 - 80 mA, though some machines may provide outputs up to 100mA. Although this is a small current, it is sufficient because the primary target for the therapy is the sensory nerves, and so long as sufficient current is passed through the tissues to depolarise these nerves, the modality can be effective.The machine will deliver pulses of electrical energy, and the rate of delivery of these pulses (the pulse rate (B) will normally be variable from about 1 or 2 pulses per second (pps) up to 200 or 250 pps. To be clinically effective, it is suggested that the TENS machine should cover a rate from about 2 150Hz.In addition to the stimulation rate, the duration (or width) of each pulse (C) may be varied from about 40 to 250 micro seconds (ms). (a micro second is a millionth of a second). Recent evidence would suggest that this is possibly a less important control that the intensity or the frequency.In addition, most modern machines will offer a BURST mode (D) in which the pulses will be allowed out in bursts or trains, usually at a rate of 2 - 3 bursts per second. Finally, a modulation mode (E) may be available which employs a method of making the pulse output less regular and therefore minimising the accommodation effects which are often encountered with this type of stimulation.The reason that such short duration pulses can be used to achieve these effects is that the targets are the sensory nerves which tend to have relatively low thresholds ( i.e. they are quite easy to excite) and that they will respond to a rapid change of electrical state. There is generally no need to apply a prolonged pulse in order to force the nerve to depolarise, therefore stimulation for less than a millisecond is sufficient.Most machines offer a dual channel output - i.e. two pairs of electrodes can be stimulated simultaneously. In some circumstances this can be a distinct advantage, though it is interesting that most patients and therapists tend to use just a single channel application.The pulses delivered by TENS stimulators vary between manufacturers, but tend to be asymmetrical biphasic modified square wave pulses. The biphasic nature of the pulse means that there is usually no net DC component, thus minimising any skin reactions due to the build up of electrolytes under the electrodes.Mechanism of Action :The type of stimulation delivered by the TENS unit aims to excite (stimulate) the sensory nerves, and by so doing, activate specific natural pain relief mechanisms. For convenience, if one considers that there are two primary pain relief mechanisms which can be activated : the Pain Gate Mechanism and the Endogenous Opioid System, the variation in stimulation parameters used to activate these two systems will be briefly considered.Pain relief by means of the pain gate mechanism involves activation (excitation) of the A beta sensory fibres, and by doing so, reduces the transmission of the noxious stimulus from the c fibres, through the spinal cord and hence on to the higher centres. The A beta fibres appear to appreciate being stimulated at a relatively high rate (in the order of 90 - 130 Hz or pps). It is difficult to find support for the concept that there is a single frequency that works best for every patient, but this range appears to cover the majority of individuals.An alternative approach is to stimulate the A delta fibres which respond preferentially to a much lower rate of stimulation (in the order of 2 - 5 Hz), which will activate the opioid mechanisms, and provide pain relief by causing the release of an endogenous opiate (encephalin) in the spinal cord which will reduce the activation of the noxious sensory pathways.A third possibility is to stimulate both nerve types at the same time by employing a burst mode stimulation. In this instance, the higher frequency stimulation output (typically at about 100Hz) is interrupted (or burst) at the rate of about 2 - 3 bursts per second. When the machine is on, it will deliver pulses at the 100Hz rate, thereby activating the A beta fibres and the pain gate mechanism, but by virtue of the rate of the burst, each burst will produce excitation in the A delta fibres, therefore stimulating the opioid mechanisms. For some patients this is by far the most effective approach to pain relief, though s a sensation, numerous patients find it less acceptable than the other forms of TENS.TENS ModesTraditional TENS (Hi TENS, Normal TENS)Usually use stimulation at a relatively high frequency (90 - 130Hz) and employ a relatively narrow pulse width (start at about 100ms) though as mentioned above, there is less support for manipulation of the pulse width in the current research literature. The stimulation is delivered at normal intensity - definitely there but not uncomfortable. 30 minutes is probably the minimal effective time, but it can be delivered for as long as needed. The main pain relief is achieved during the stimulation, with a limited carry over effect i.e. pain relief after the machine has been switched off. Acupuncture TENS (Lo TENS, AcuTENS)Use a lower frequency stimulation (2-5Hz) with wider (longer) pulses (200-250ms). The intensity employed will usually need to be greater than with the traditional TENS - still not at the patients threshold, but quite a definite, strong sensation. As previously, something like 30 minutes will need to be delivered as a minimally effective dose. It takes some time for the opioid levels to build up with this type of TENS and hence the onset of pain relief may be slower than with the traditional mode. Once sufficient opioid has been released however, it will keep on working after cessation of the stimulation. Many patients find that stimulation at this low frequency at intervals throughout the day is an effective strategy. The carry over effect may last for several hours.Brief Intense TENS :This a TENS mode that can be employed to achieve a rapid pain relief, but some patients may find the strength of the stimulation too intense and will not tolerate it for sufficient duration to make the treatment worthwhile. The pulse frequency applied is high (in the 90-130Hz band) and the pulse width is also high (200ms plus). The current is delivered at, or close to the tolerance level for the patient - such that they would not want the machine turned up any higher. In this way, the energy delivery to the patients is relatively high when compared with the other approaches. It is suggested that 15 - 30 minutes at this stimulation level is the most that would normally be used. Burst Mode TENS :As described above, the machine is set to deliver traditional TENS, but the Burst mode is switched in, therefore interrupting the stimulation outflow at rate of 2 - 3 bursts / second. The stimulation intensity will need to be relatively high, though not as high as the brief intense TENS more like the lo TENS.Return to Top Frequency Selection :With all of the above mode guides, it is probably inappropriate to identify very specific frequencies that need to be applied to achieve a particular effect. If there was a single frequency that worked for everybody, it would be much easier, but the research does not support this concept. Patients (or the therapist) need to identify the most effective frequency for their pain, and manipulation of the stimulation frequency dial or button is the best way to achieve this. Patients who are told to leave the dials alone are less likely to achieve optimal effects.Stimulation Intensity :As identified above, it is not possible to describe treatment current strength in terms of how many microamps. The most effective intensity management appears to be related to what the patient feels during the stimulation, and this may vary from session to session. As a general guide, it appears to be effective to go for a definitely there but not painful level for the normal (high) TENS, and a strong but not painful level for the acupuncture (lo) mode.Electrode placement :In order to get the maximal benefit from the modality, target the stimulus at the appropriate spinal cord level (appropriate to the pain). Placing the electrodes either side of the lesion or pain areas, is the most common mechanism employed to achieve this. There are many alternatives that have been researched and found to be effective most of which are based on the appropriate nerve root level :Stimulation of appropriate nerve root(s) Stimulate the peripheral nerve Stimulate motor point Stimulate trigger point(s) or acupuncture point(s) Stimulate the